Data embedding is a technique for adding a representation of information into an article, such as a letter or a banknote. A special case of data embedding is steganography, which is the science and art of secret communication. In steganography, the presence of a hidden message typically needs to be concealed in a signal, despite the fact that the signal must be altered to enable the embedding. In physically printed, or rendered content, however, a different approach to data embedding is possible. For example, a data-bearing pattern may be achieved by manipulating a halftone rendering engine. In a data-bearing halftone, data is embedded in a halftone printed output by shifting certain output spatial element values, e.g. in two-dimensions shifting certain pixel values from 0 to 1. Another case of data hiding is watermarking, where it may be desired to determine the authenticity of a book or certificate. In this case, the presence of a watermark may indicate authenticity, while the absence of a watermark may indicate a forgery. When watermarking a printed output there may be a challenge of avoiding an active adversary that would attempt to remove, invalidate or forge watermarks in digital content. Another example of data embedding involves quick response (QR) codes, which provide machine-readable codes that are visible and may be used to convey information such as uniform resource locators.